1. Field of the Invention
The present invention relates to a scanning apparatus for scanning objects with a wave propagation beam such as a laser beam, an electromagnetic wave beam, an acoustic wave beam or the like.
2. Description of Related Art
There is known heretofore a scanning apparatus of the structure mentioned below. That is, a scanning mechanism for a scanner for reading a bar code located at a distant position by scanning the bar code transversely with a light beam, wherein the scanning mechanism is comprised of a mirror for angularly displacing or deflecting the light beam so that the bar code can be scanned with the light beam, and a plate spring which supports the mirror reciprocatively rotatably or swingably. To this end, the plate spring is bent in a chevron-like form with the mirror being fixedly secured at the bent portion of the chevron-like plate spring.
By applying a force to a planar or flat portion on one side of the chevron-like plate spring by means of an electromagnet, the mirror is reciprocatively rotated or swung. By selecting the position of a split pin defining the center of rotation or swinging of the mirror so as not to coincide with the point of application of the force applied to the plate spring by the electromagnet, the force of the electromagnet is converted into reciprocative rotating or swinging efforts. For more particulars, reference may be made to, for example, Japanese Patent Application Laid-Open Publication No. 139836/1994(JP-A-6-139836).
In the scanning apparatus known heretofore, the plate spring bent in the chevron-like shape is made use of. In such plate spring, it is desirable that planar portions formed on both sides of the bent position be each of a perfect plane. In practice, however, it is difficult or impossible to realize the perfect plane in view of the limitation imposed to the manufacturing precision. Usually, the planar portion assumes such a shape that a mid portion bulges out three dimensionally more or less. When such plate spring undergoes a bending or flexing deformation, a shot-like discontinuous force will be generated upon flexing beyond the vicinity of a neutral position, which makes it difficult to realize a smooth vibratory or reciprocatively rotation or swinging of the deflector, giving rise to a problem.
Further, the bent portion is formed substantially at a center of the plate spring and the mirror is mounted at this position. Consequently, for realizing the scanning apparatus, there is demanded a press work of high precision, giving rise to another problem. Additionally, because the plate spring is shaped in the chevron-like form, an extraneous space is required for accommodation of the plate spring, i.e., the scanning apparatus can not be implemented in a small size as desired.